Recently, with enhancement of sensitivity and image quality of silver halide light-sensitive color photographic material have brought customers of color photographic materials advantages that the chance of blunders in the picture-taking due to blurring has been reduced and chances of shooting have been enlarged. Thus, for example, it became possible to catch a subject with a swift movement, and shooting in a dimly-lit place became possible.
Under such a background situation, it may be said that customer's expectation that the pictures with the best finishing are always obtainable whenever and wherever they feel to record as photographic pictures, has been increasing.
In order to answer such a expectation of customers, various efforts have been made by photo-laboratories so that they can deliver as best prints as possible, However, in view of the yield of very best finished prints, the present status may not be the best, as well as from the ecomomical point of view. Therefore, further improvement in this respect has been demanded.
Various causes has been considered for this. According to the research by the present inventors, it has been revealed that improvement in the color negative films used at the time of picture-takinging would greatly contribute to the improvement in print yield.
That is to say, situations, under which the photographic materials are used, are so various that they are not always provided for use without leaving a long time after manufacture thereof. Depending on the customer it is not unusual that customers use the photographic material after lapse of the term of validity thereof. Further, there is no regular pattern as to the period the customers bring the photographic materials to a photo-finishing laboratory. Therefore, color negative films which are capable of producing prints with enhanced and constant image quality, without reducing print loss or yield even if they are used and processed under different conditions.
In order to answer these demands, technologies for improving the stability such as latent image stability or aging stability have been proposed and known in the art. For example, a method of using a benzthiazolium salt for the purpose of improving the latent image stability is disclosed in Japanese Patent O.P.I. Publication No. 50-94918(1975), and for the enhancement of the aging stability, Japanese Patent O.P.I. Publication Nos. 2-108038(1990) and 3-194540(1991) disclose a method of using an oxidizing agent of silver such as a thiosulfonate. However, these techniques individually cannot be a dominant factor for the improvement of the print yield. Further the target could not be attained even by combining these techniques.
Japanese Patent O.P.I. Publication Nos. 3-235942(1991) and 3-240051(1991) disclose a technique of improving the printing yield by using a core/shell-type silver halide grain emulsion and regulating sensitometric properties thereof. According to this technique, the effect of enhancement in the printing yield was attained in the case where the photographic material is used and processed within the term of validity; however, the effect is still insufficient and a serious problem that the print yield is remarkably lowered especially in the case when the photographic material was left unprocessed for a long time after picture-taking.